Integrated circuit dies conventionally are enclosed in semiconductor packages that provide protection from hostile environments and enable electrical interconnection between the integrated circuit die and an underlying substrate, such as a leadframe or printed circuit board (PCB). In semiconductor packages using a leadframe, the leadframe is the central supporting structure of the semiconductor package. A portion of the leadframe is internal to the package, i.e., completely surrounded by an encapsulant.
For purposes of high-volume, low-cost production of semiconductor packages, a current industry practice is to etch or stamp a thin sheet of metal material to form a panel or strip that defines multiple leadframes. A single strip may be formed to include multiple arrays, with each such array including a multiplicity of leadframes in a particular pattern. In a typical semiconductor package manufacturing process, the integrated circuit dies are mounted and wire bonded to respective ones of the leadframes, with the encapsulant material then being applied to the strips to encapsulate the integrated circuit dies, bond wires, and portions of each of the leadframes.
Varieties of techniques are known for interconnecting an integrated circuit die to a substrate. These techniques include wire bonding, tape automated bonding (TAB), and flip chip bonding. In wire bonding, a bond pad on an integrated circuit die is attached to a contact on a substrate or other microelectronic component. In the case of leadframes as substrates, the contact is referred to as a lead finger. In forming the wire bond, a bonding wire is fed through a capillary, which is guided under computer control. A ball of molten wire is formed at the tip of the wire. The ball is then pressed against the bond pad of the integrated circuit die or the contact of the substrate, forming a “bump bond.” Most commonly, the bump bond is formed on the bond pad of the integrated circuit die rather than on the contact of the substrate although it can be on either.
The other end of the bonding wire typically is attached to the contact of the substrate using a “stitch bond.” In a stitch bond, ultrasonic energy is delivered to the wire through the capillary as the capillary presses the wire against the contact of the substrate. A bonding head carrying the capillary is retracted to leave a wire tail at the stitch. Thereafter, a wire clamp carried by the bonding head is closed, tearing the wire as the bonding head retracts further.
In conventional chip-on-board (COB) structures, an integrated circuit chip or other microelectronic component is attached to a substrate with the active surface of the microelectronic component facing outwardly away from the substrate. The back surface of the microelectronic component is adhesively bonded to the substrate. The bond pads on the microelectronic component may then be wire bonded to lead fingers or contacts arranged on the surface of the substrate to electrically couple the microelectronic component to the substrate. The bonding wire may extend laterally outwardly away from a stitch bond rather than generally perpendicularly outwardly, as is the case in a bump bond. The minimum height of a stitch bond, consequently, can be significantly smaller than a bump bond, being limited primarily by the thickness of the bonding wire.
As the trend toward smaller semiconductor packages increases, there is a need for higher wire density in a semiconductor package. Bond pads on the integrated circuit die have been formed smaller than or equal to about 45 microns to increase density, but there has been difficulty in manufacturing a leadframe with fine pitch lead fingers. Consequently, lead fingers have remained at a width of about 90 microns to accommodate the tolerances involved in stitch bonding bond wires to the lead fingers. Additionally, the upper surfaces of the lead fingers are not always flat thereby making it difficult to perform a stitch bond onto the lead fingers. Accordingly, there has been no acceptable solution for manufacturing a semiconductor package having lead fingers on a leadframe with a fine pitch.
Solutions to these problems have been long sought but prior developments have not taught or suggested any solutions and, thus, solutions to these problems have long eluded those skilled in the art.